<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        /* 因为div没有边框 */
        div{
            width: 200px;
            height: 200px;
            background-color:red;
            /* position: absolute; */
            /* float: left; */
            /* border: solid red; */
        }
        div p{
            width: 50px;
            height: 50px;
            background-color: blue;  
            margin-top: 100px;
        }
    </style>
</head>
<body>
    <div>
        <p></p>
    </div>
</body>
</html>